Effects of residual stresses on fatigue resistance in torsion with bending in the presence of stress concentrations

Fatigue-test results are given for torsion with bending in cylindrical steel 45 specimens having small semicircular profile notches and with and without residual stresses. The effects of hardening on the fatigue resistance are evaluated from a residual-stress criterion. The test data for the unhardened and hardened specimens are closely described by the equation of an ellipse, which enables one to express the margin coefficient in torsion with bending with allowance for the residual stresses.Translated from Problemy Prochnosti, No. 12, pp. 37–40, December, 1992.     

光弹性复合材料应变-光定律研究

本文在考察Agawal近似应变——光定律的基础上,提出了新的近似应变——光定律.它克服了Agawal近似应变——光定律当主应变分向靠近材料主方向时产生较大误差的弊病,提高了复合材料光弹性近似分析的精度,为复合材料正变异性光弹性分析的工程应用奠定了基础.     

Determination of the particulate extinction-coefficient profile and the column-integrated lidar ratios using the backscatter-coefficient and optical-depth profiles

A new method is considered that can be used for inverting data obtained from a combined elastic-inelastic lidar or a high spectral resolution lidar operating in a one-directional mode, or an elastic lidar operating in a multiangle mode. The particulate extinction coefficient is retrieved from the simultaneously measured profiles of the particulate backscatter coefficient and the particulate optical depth. The stepwise profile of the column-integrated lidar ratio is found that provides best matching of the initial (inverted) profile of the optical depth to that obtained by the inversion of the backscatter-coefficient profile. The retrieval of the extinction coefficient is made without using numerical differentiation. The method reduces the level of random noise in the retrieved extinction coefficient to the level of noise in the inverted backscatter coefficient. Examples of simulated and experimental data are presented.     

Effect of CO2 laser irradiation on the refractive-index change in optical fibers

The effect of CO2 laser irradiation on the refractive-index change in optical fibers is investigated by measuring the interference fringe shift formed by a long-period fiber grating pair. The refractive-index decrease on CO2 laser irradiation was due to relaxation of the residual stress, which was formed in optical fibers during the drawing process, and the refractive-index decrease was found to increase linearly with the drawing force. The effect of the CO2 laser output power on residual-stress relaxation, and fiber elongation was also studied.     

Transient-temperature and residual-stress fields in axisymmetric metal components after hardening

Abstract

A finite-element method is used to analyse the transient–temperature and residual-stress fields in an axisymmetric metal specimen during quenching. In the calculation of transient-temperature fields it is assumed that an unsteady source of latent heat exists in the specimen when a phase transformation occurs. Factors such as the surface heat transfer coefficient, heat conductivity coefficient, linear expansion coefficient, density, specific heat capacity, latent heat, and so forth are all temperature dependent. The elastic-plastic properties of the specimen are modified according to temperature fields, which are determined; the influence of plastic deformation on the temperature fields is neglected. The agreement between the calculated results and the experimental data shows that the numerical analysis method is reliable. The method may also be applied to the analysis of specimens with other than axisymmetric shape.

MST/15     

Embedded fiber-optic Fabry-Perot ultrasound sensor

A fiber-optic ultrasound sensor is presented. The sensor consists of a continuous length of single-mode optical fiber with a built-in Fabry-Perot interferometer. The acoustic pressure produces changes in the index of refraction along the interferometer cavity through the strain-optic effect, thus modulating the reflected power of the light propagating in the fiber. The dielectric internal mirrors that form the interferometer are fabricated by joining a fiber coating with a TiO(2) film at one end to an uncoated fiber by electric arc fusion splicing. Experimental results have been obtained for sensors embedded in plastic and graphite composite materials, using ultrasound waves in the range from 100 kHz to 5 MHz. Values for the optical phase shift amplitude as large as 0.5 rad were obtained at an acoustic frequency of 200 kHz for a 1.1-cm-long interferometer embedded in plastic.     

Characterization of strong fiber Bragg gratings using an applied thermal chirp and iterative algorithm

Coupling coefficients of various grating types and strengths are calculated from measurements of the complex reflectivity using an applied thermal chirp and optical frequency domain reflectometry (OFDR). The complex reflectivity is then utilized by a layer peeling algorithm to determine the coupling coefficient of the thermally chirped grating. A guess of the temperature profile enables the coupling coefficient of the unchirped grating to be estimated. An iterative algorithm is then used to converge on the exact coupling coefficient, employing an error minimization method applied to the reflectivity spectra. This technique removes the need for a reference grating while preserving the spatial resolution obtained with the initial OFDR measurement. Successful reconstruction of gratings with integrated |κ|L ~ 9.0 are demonstrated with a spatial resolution of less than 100 μm.     

External-cavity diode lasers with different devices and collimating optics

Comparative operating characteristics of external-cavity diode lasers (ECDL's) with either a channel substrate planar device or a multi-quantum-well (MQW) device are presented. These include the output beam profile, which is significantly altered depending on the collimating lens used (either multielement or graded index), power versus injection-current characteristics, and the optical frequency and the rf spectra. The coherence lengths of the different laser diode-collimating-lens combinations in the ECDL are measured, and a new method for calculating the coupling coefficient and the coupled values of the internal quantum efficiency and the internal lumped loss is demonstrated for the MQW device.     

Dual beam light profile microscopy: a new technique for optical absorption depth profilometry

Light profile microscopy (LPM) is a recently developed technique of optical inspection that is used to record micrometer-scale images of thin-film cross-sections on a direct basis. In single beam mode, LPM provides image contrast based on luminescence, elastic, and/or inelastic scatter. However, LPM may also be used to depth profile the optical absorption coefficient of a thin film based on a method of dual beam irradiation presented in this work. The method uses a pair of collimated laser beams to consecutively irradiate a film from two opposing directions along the depth axis. An average profile of the beam's light intensity variation through the material is recovered for each direction and used to compute a depth-dependent differential absorbance profile. This latter quantity is shown from theory to be related to the film's depth-dependent optical absorption coefficient through a simple linear model that may be inverted by standard methods of numerical linear algebra. The inverse problem is relatively well posed, showing good immunity to data errors. This profilometry method is experimentally applied to a set of well-characterized materials with known absorption properties over a scale of tens of micrometers, and the reconstructed absorption profiles were found to be highly consistent with the reference data.     

Concurrent three-dimensional characterization of the refractive-index and residual-stress distributions in optical fibers

A three-dimensional index-stress distribution (3DISD) measurement method for determining concurrently the refractive-index distributions (RIDs) and residual-stress distributions (RSDs) in optical fibers is presented. The method combines the quantitative-phase microscopy technique, the Brace-K?hler compensator technique, and computed tomography principles. These techniques are implemented on a common apparatus to enable concurrent characterization of the RID and the RSD. Measurements are performed on Corning SMF-28 fiber in an unperturbed section and in a section exposed to CO₂ laser radiation. The concurrent measurements allow for the first accurate comparison of the collocated RID and RSD. The resolutions of the refractive index and stress are estimated to be 2.34×10^-5 and 0.35?MPa, respectively.     

Depth profiling of the optical absorption coefficient in ultraviolet-degraded poly(vinylchloride) films by dual beam light profile microscopy

Dual beam laser light profile microscopy (LPM) was applied in this work to the depth mapping of the optical absorption coefficient in photo-degraded poly(vinyl chloride) films. Depth profiles followed the absorption coefficient of a conjugated polyene photoproduct at visible wavelengths in photolyzed films of approximately 200 mum thickness. Both continuous and layered (separable laminate) films were studied. The absorption coefficient profiles reconstructed from photo-degraded thin films showed the classic concentration profiles seen in the literature for PVC degraded in the presence of oxygen and nitrogen atmospheres. In the case of single thin layers with continuous properties, the depth profiles were smooth and regular with minimum spatial noise. In the LPM of laminate structures, more optical anomalies were present because of the multiply interfacial structures that appeared in both the images and the reconstructed depth profiles. Notwithstanding, it was possible to profile the optical absorption coefficient at a level of error comparable to standard microtome methods. The latter was determined by comparing the LPM results to a destructive layer-by-layer analysis performed in parallel on the imaged materials. The dual beam LPM method should be generally useful for establishing polyene concentration profiles in industrial materials produced by photochemical, thermal, and chemical degradation mechanisms.     

Investigation of thermal annealing of optical properties and residual stress of ion-beam-assisted TiO2 thin films with different substrate temperatures

Titanium oxide films were prepared by ion-beam-assisted deposition on glass substrates at various substrate temperatures. The effect of the temperature of thermal annealing from 100 degrees C to 300 degrees C on the optical properties and residual stress was investigated. The influence on the stoichiometry and residual stress of titanium oxides deposited at different substrate temperature was discussed. The residual-stress was minimum and the extinction coefficient was maximum at an annealing temperature of 200 degrees C with a substrate temperature of 150 degrees C. However, when the substrate temperature was increased to 200 degrees C and 250 degrees C, the residual stress was minimum and the extinction coefficient was maximum at an annealing temperature of 250 degrees C. The spectra of x-ray photoelectron spectroscopy reveal that the films lost oxygen and slowly generated lower suboxides at the annealing temperature at which the residual stress was minimum and the extinction coefficient was maximum. As the annealing temperature increased above the temperature at minimum stress, the lower suboxides began to capture oxygen and form stable oxides. TiO2 films deposited at substrate temperatures of 200 degrees C and 250 degrees C were more stable than films deposited at 150 degrees C.     

Fluorescence spectroscopy of tissue: recovery of intrinsic fluorescence from measured fluorescence

We present a method for recovering the intrinsic fluorescence coefficient, defined as the product of the fluorophore absorption coefficient and the fluorescence energy yield, of an optically thick, homogeneous, turbid medium from a surface measurement of fluorescence and from knowledge of medium optical properties. The measured fluorescence signal is related to the intrinsic fluorescence coefficient by an optical property dependent path-length factor. A simple expression was developed for the path-length factor, which characterizes the penetration of excitation light and the escape of fluorescence from the medium. Experiments with fluorescent tissue phantoms demonstrated that intrinsic fluorescence line shape could be recovered and that fluorophore concentration could be estimated within ±15%, over a wide range of optical properties.     

Synthesis of symmetric and asymmetric planar optical waveguides

A novel and accurate refractive index profile synthesis method for planar optical waveguides is presented and demonstrated using the transmitted near-electric-field-data. This method is based on the inverse transmission-line (TL) technique. From Maxwell's equations, a TL equivalent circuit (electric T-circuit) for the refractive index profile of a planar optical waveguide is derived. The authors demonstrate how to use this model to carry out the inverse problem and synthesise the exact refractive index profile numerically from near-field-data. The TL method can reconstruct arbitrary refractive index profiles for planar optical waveguides that support singlemode or multi- modes. The cases of both symmetric and asymmetric arbitrary refractive index profile planar waveguides are discussed. The accuracy of the reconstructed waveguides is examined numerically.     

Optical electromagnetic vector-field modeling for the accurate analysis of finite diffractive structures of high complexity

An electromagnetic vector-field model for design of optical components based on the finite-difference time-domain method and radiation integrals is presented. Its ability to predict the optical electromagnetic dynamics in structures with complex material distributions is demonstrated. Theoretical and numerical investigations of finite-length surface-relief structures embedded in polymer dielectric waveguiding materials are presented. The importance of several geometric parameter dependencies is indicated as far-field power distributions are rearranged between diffraction orders. The influences of the variation in grating period, modulation depth, length, and profile are investigated.     

Reconstruction method with data from a multiple-site continuous-wave source for three-dimensional optical tomography

A method is presented for reconstruction of the optical absorption coefficient from transmission near-infrared data with a cw source. As it is distinct from other available schemes such as optimization or Newton's iterative method, this method resolves the inverse problem by solving a boundary value problem for a Volterra-type integral-differential equation. It is demonstrated in numerical studies that this technique has a better than average stability with respect to the discrepancy between the initial guess and the actual unknown absorption coefficient. The method is particularly useful for reconstruction from a large data set obtained from a CCD camera. Several numerical reconstruction examples are presented.     

Dwell function algorithm in fluid jet polishing

Considering the special characteristics of the removal function with the ring-shaped profile in fluid jet polishing (FJP), we present an effective method called the discrete convolution algorithm to compute the dwell function for controlling the figuring process. This method avoids the deconvolution operation, which usually fails to converge. Then an experimental confirmation of FJP figuring was demonstrated by machining a one-dimensional depth profile on a flat sample. The profile was figured from 0.914lambda(lambda=632.8 nm) peak to valley (PV) to 0.260lambda. This experiment demonstrated the successful implementation of the algorithm to solve the dwell function in optical manufacturing.     

Increasing the working range of coherent optical time-domain reflectometer

A new method for increasing the working range of a coherent optical time-domain reflectometer (COTDR) has been theoretically justified and experimentally demonstrated. The proposed method is based on the use of several types of optic fibers with different backscatter coefficients, in which the fiber with a higher backscatter coefficient is connected to the end of a fiber with the minimum absorption coefficient at the working wavelength, the length of which is the maximum possible in order to ensure a preset sensitivity level. It is shown that, using this approach, the COTDR working range can be increased up to 50 km.     

Optical properties of an optically rough coating from inversion of diffuse reflectance measurements

A method is developed for determining the optical properties of an optically rough coating on an opaque substrate from reflectance measurements. A modified Kubelka-Munk two- flux model is used to calculate the reflectance of the coating as a function of the refractive index, absorption coefficient, scattering coefficient, and thickness. The calculated reflectance is then fitted to measurements using a spectral projected gradient algorithm, allowing the optical properties to be obtained. The technique is applied to titanium dioxide coatings on a titanium substrate. Realistic values of refractive index and absorption coefficients are generally obtained. Quantities that are useful for solar water-splitting applications are calculated, including the depth profile of absorption and the proportion of the incident photon flux absorbed in the coating under solar illumination.     

A brief review of photo-orthotropic elasticity theories

The development of the theory of birefringence of annotropic composites has proceeded mainly along the following directions, strew strain models, analogy, integrated photoelasticity and tensonal nature of birefringence. All these studies have concluded that three independent photoelastic constants are needed to characterize orthotropic model materials. In the literature, there has not been uniformity of notation used in the representations of the results. In this paper, using uniform notation, existing photo-orthotropic clasticity theories are reviewed under three major headings stress-optic laws strain-optic laws and approximate strain-optic laws. The interrelation ships between stress-optic and strain-optic coefficients are brought out Interpretation of isoclinics is discussed. The steps necessary to calibrate a birefringent orthotropic composite are summarized and finally the influence of residual birefringence is also discussed.